Organic redox flow batteries are particularly attractive for meeting the demanding performance, cost and sustainability requirements for grid-scale energy storage. It is widely known that the intermittency of renewable energy generation from solar and wind resources necessitates that large-scale energy storage be available for load-shifting or peak-shaving on the grid, at sub-station, and even at residences. With an estimated global electricity production of about 50-60 TeraWatt hours/day, even if only 20% of this energy is stored, deployment of 10-15 Gigatons of batteries over a 15 year period assuming a modest specific energy of 50 Wh/kg is required. A point of reference for the scale of assessing this demand is that it is five times as large as the world's iron and steel industry in that 2.8 Gigatons of iron ore is mined every year worldwide. The astonishing magnitude of this demand for batteries for grid-scale energy storage imposes the most stringent requirements not only on cost and durability, but also on eco-friendliness and sustainability. The requirement of eco-friendliness and sustainability has only been recently emphasized in the Department of Energy's approach to new technology solutions.
The capital cost of a battery system is largely determined by the materials cost, complexity of the system design, and performance features such as—energy density, power density, durability, and efficiency. Sustainability is determined by resource limitations, eco-friendliness of the manufacturing and recycling processes. Although some of the more mature systems like vanadium redox and zinc-chlorine are gradually moving towards large-scale implementation, the high associated expenses mandate cost reductions. Moreover, some of the prior art battery technologies use heavy metals such as vanadium and/or chromium which are environmentally undesirable. Iron-air and manganese dioxide-carbon systems are promising from a cost and sustainability standpoint. However, these technologies are not based on renewable resources thereby rendering their long term sustainability uncertain. It should be appreciated that a battery based on carbon resources that avoids the use of metals can provide long-term sustainability in addition to being inexpensive.
Accordingly, there is a need for improved redox flow battery systems that are eco-friendly while using inexpensive material.